The present invention provides an improved method of removing NO from a regenerated ferric sulfate solution formed in the presence of NO.
As is explained in the inventor's co-pending application, ferric sulfate has the ability to react with H.sub.2 S to form elemental sulfur, sulfuric acid, and ferrous sulfate in the following reaction: EQU H.sub.2 S+Fe.sub.2 (SO.sub.4).sub.3 =2FeSO.sub.4 +H.sub.2 SO.sub.4 +S
To use this reaction in a commercial operation, it is necessary to economically regenerate the ferric sulfate from the sulfuric acid and ferrous sulfate.
Although the least costly oxidant is oxygen in air, elemental oxygen is not capable of performing the regeneration. However, as the previous application explained, in the presence of NO, oxygen can accomplish this overall reaction. The effective reactions are: EQU (1) 2NO+O.sub.2 =2NO.sub.2 EQU (2) 2 FeSO.sub.4 +H.sub.2 SO.sub.4 +NO.sub.2 =NO+Fe.sub.2 (SO.sub.4).sub.3 +H.sub.2 O
The NO formed in reaction (2) can then react with additional oxygen as shown in reaction (1).
Although it is usually advantageous to carry out the regeneration reaction at an elevated pressure to increase the rate of reaction (1), at such pressure the ferric sulfate solution, which may already contain unoxidized ferrous sulfate, will also contain dissolved NO. If the ferric sulfate solution is not substantially free from dissolved NO prior to the solution's contact with the H.sub.2 S containing gas, the NO will leave the solution and contaminate the H.sub.2 S-free gas. This limits the potential use of such gas and wastes the NO contained therein.
Until the present invention, the seriousness and wastefulness of creating and releasing such NO contaminated gas has not been appreciated.
Accordingly, it is a primary object of the present invention to remove NO from the ferric sulfate solution and to avoid contamination of H.sub.2 S-free gas.
It is a further object of the present invention to recover such NO and recycle it for the further regeneration of ferric sulfate.